The present invention relates to a fastening structure for fastening a bolt to a flange by press-fitting a serration of the bolt into a bolthole of the flange.
There has conventionally been a mechanism as shown in FIG. 4, which adopts this kind of fastening structure. This structure is a structure for fastening a brake disk 103 and a wheel member 110 to a flange 102 of an inner ring member 105 by means of a bolt 101 and a nut 111.
According to this fastening structure, the bolt 101 is fixed to the flange 102 by press-fitting a serration 106 formed on the bolt 101 into a bolthole 107 of the flange 102. Then, the brake disk 103 and the wheel member 110 are fitted around this bolt 101 and fastened by means of the nut 111.
However, in the aforementioned conventional fastening structure, as shown in FIG. 3, an inner peripheral surface 107A of the bolthole 107 of the flange 102 is pressed by the serration 106 when the bolt 101 is press-fit into the flange 102, so that the flange 102 is elastically deformed. Due to this elastic deformation, a flange surface 102A on the bolt head side is deformed into a convex shape, while a flange surface 102B on the opposite side is deformed into a concave shape.
As described above, if the flatness of the flange surfaces 102A and 102B are deteriorated, then the brake disk 103 cannot be mounted parallel to the flange surface 102B. This leads to the problem that one-sided abutment of the brake disk 103 is caused, generating vibrations and abnormal noises.
Accordingly, the object of the present invention is to provide a fastening structure capable of preventing the deterioration in flatness of the flange surface when the serration of the bolt is press-fit into the flange.
In order to achieve the aforementioned object, the present invention provides a fastening structure including a bolt whose one portion in an axial direction of an outer peripheral surface is provided with a serration is press-fit into a bolthole formed in a flange portion of a mounting member.
A first distance between one axial end portion of the serration and one end surface of the flange portion exceeds 13% of a thickness in the axial direction of the flange portion, and a second distance between the other axial end portion of the serration and the other end surface of the flange portion exceeds 13% of the thickness in the axial direction of the flange portion.
According to the fastening structure of the present invention, the serration is located apart from the respective end surfaces of the flange portion by the first and second distances, and the first and second distances each exceed 13% of the thickness of the flange portion. With this arrangement, when the bolt is press-fit into the flange portion, the serration presses the bolthole inner peripheral surface only in a region far from both the end surfaces of the flange portion (in a region deeper than 13% of the thickness). In the regions close to the respective end surfaces of the flange portion (in each region shallower than 13% of the thickness), the serration does not press the bolthole inner peripheral surface.
By thus limiting the region where the serration of the bolt presses the bolthole inner peripheral surface to the region located far apart from both the end surfaces of the flange portion, the flange surface can be prevented from deteriorating in flatness when the serration is press-fit into the flange.
In an embodiment, a center portion in the axial direction of the serration substantially coincides with a center portion in the axial direction of thickness of the flange portion.
In this embodiment, the center portion in the axial direction of the serration is made to substantially coincide with the center portion in the direction of thickness of the flange portion. With this arrangement, the dimension in the axial direction of the serration can be maximized with the flatness of the flange surface maintained, thereby allowing its slip torque to be maximized.